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Offline digger1Topic starter
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« Reply #10 on: April 15, 2009, 12:39:47 pm »
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Hate to chat and run but I am going digging for a few hours!

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Offline Christian
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« Reply #11 on: April 15, 2009, 01:18:46 pm »
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Well, 20 feet is quite a bit. This might be too much for the magnetometer. I unfortunately can't say for sure. However as it seems a magnetometer would probably be your best bet to find it.

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Christian

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Offline digger1Topic starter
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« Reply #12 on: April 15, 2009, 04:58:17 pm »
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Hello Christian,
That is my thinking also!

Maybe that is why it is still misssing, no one can figure out where it is because it is to deep for metal detectors even the 2 box type.
Thanks
digger1

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« Reply #13 on: May 01, 2009, 12:14:20 am »
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A good PPM would easily locate a cannon made of iron 12ft deep. We have the proof that it is able to locate an ammo box of 7.5Kg at 3 meters (9ft) and a cannon should weight much, much more.
See the document : 'Benchmark test results' located at URL

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Good luck,
Willy

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« Last Edit: May 01, 2009, 12:16:09 am by willy bayot »
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Offline willy bayot
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« Reply #14 on: May 01, 2009, 10:02:02 am »
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Just my little contribution on this topic:

A PPM measures the total earth magnetic field. This is unlike a fluxgate mag which measures a single of its three vectors at a time.
Thus, the fluxgate is VERY directional by physical laws but the PPM is not.
However, it is true that some kinds of PPM sensor configurations are themselves giving higher or lower precession signals when oriented on certain directions but, if the SNR of the mag is good enough and the sensor coils are correctly oriented on the horizontal plan, the differences of signal quality when the sensor is oriented on the worst direction are not giving any problem.
In summary, a double solenoid coil sensor can be oriented in any directions if its main axis is kept horizontal in western latitudes or vertical in the equatorial regions.
A toroid sensor is not directionally sensitive at all in the same conditions but it is much more difficult to build than a solenoid. That's the reason why most of the current PPM sensors used ofr underground surveys are made of double solenoid coils. The double coil helps to cancel the environmental random noise. At sea, the noise level is much lower and thus, many underwater PPM sensors are made of a single solenoid coil.
About the need of a double sensor system (gradiometer or differential configurations) or th euse of a single sensor system, it all depends on what you are looking for as potential targets.
1. You look for targets made of magnetic material generating field gradients of more than 10nT's (see the nomogram previously posted on this forum to calculate the field gradient depending on the mass and distance of the target). This is the case when looking for buried treasures supposedly contained in or close to large containers or objects made of iron
--> these field gradients will be higher than the normal diurnal variations which are measured in one or two nT's per minute except if you are so unlucky to make you survey during a magnetic storm. Thus, a PPM with a single sensor and a fast reading rate will be enough to show up the monopoles and dipoles generated by that type of targets.
2. You look for targets made of various ground types with various magnetic susceptibilty generating field gradients of the range of the diurnal variations. This is when you look for archaeological structures like foundation walls, fire pits, wells or any man-made ground disturbance.
--> In that case, you need to cancel the diurnal variations in order to make the real gradients showing up on the plots. A gradiometer will simultaneously measure the total field at two locations separated by a fixed distance (usually one to two meters). The differences between each reading will be the real field gradients. A differential configuration will give about the same result by measuring the total field at a fixed station while the mobile station makes the readings on the survey lines. the differences between the synchronized readings f the two stations give the expected result.

Willy

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« Reply #15 on: May 01, 2009, 10:06:42 am »
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Thanks for your great advice Willy!

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« Reply #16 on: June 12, 2009, 03:24:29 pm »
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Hi;
I had about a 500 or even maybe 10,000 word reply, to you but it 'timed out' since I am NEW on this forum (and it is different,) I didn't check the 'forever' box, to prevent this...

Gist of what I said is if the area soil has naturally low iron content, a magnetometer should work, as for all the time it has been buried, there will be some dispersion of ferrous ions, no matter how low the precip rate. A ravine is a moisture channel!

I still think a 2 box should do the trick. Make your own, make it with a very large coil and have it operate below 30 kilaHertz, for better penetration: 36" to 40" coil (brush may be a problem;) use a bit more power, say up to 0.5 watt; operate at 10 kHertz.

This means, you can employ a simple, sensitive mike amp kit, on the receiver coil! But it will still require a sensative preamp to match to such a kit... a grounded gate, MPS (MPF?)102, FET, should give lots of gain and match to the coil fairly well. You want a simple circuit diagram? Email me, personally and use '2 box locator' in the subject box. This item can be found at any supplier, and I won't deop names, here.

I have a simple, stable, one transistor circuit for a 2 box transmitter if anyone is interested. I will send a .GIF of it, on request. Please, forget  about "Paint," it is archaic and cannot do anything in the line of schematics. For DIY electronics, you need a better program.

Brian AKA goldigger (and I am)


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« Reply #17 on: June 12, 2009, 03:35:42 pm »
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Hi, Willy;
A 'side' word; a PPM (field type) detected anomalies, relative to the earth's field, please, do not confuse survey instruments with 'Observatory' instruments.... a totally different kettle of fish... er... gold.
Brian AKA goldigger (and I am)

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« Reply #18 on: June 12, 2009, 09:58:57 pm »
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Thanks Brian, I will email as I would like to see what you have in mind.

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« Reply #19 on: June 13, 2009, 01:19:16 am »
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Hi Brian,

A PPM can be used both as fixed observatory station to capture the earth field variations in order to predict the magnetic storms AND used as field survey instrument capturing and plotting magnetic field gradients generated by buried or sunk targets made of magnetic material.
We are successfully using this type of instrument in our archaeological surveys and other people use it for detecting the anchor or the cannons of old sunken boats.

Willy



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